Smurfy, here is what you do. Take a half cup of plain oats and put them in a coffee bean grinder, grind them to dust. Then add to your shake, this way you're getting some complex carbs with your protein. Or even throw in a bannana and like I said before, some fat free peanut butter. Fat free yogurt is good as well, sometimes I do this to break the monotony.
I also have a great tuna shake recipe if you're interested